Long-term trends of atmospheric circulation over Europe: Comparison of three secular datasets and six recent reanalyses

• Main Author: Cahynová, M. (Monika)
• Format: Other/Unknown Material
• Language: English
• Published: 2015
• Subjects: atmospheric circulation; climatic trends; North Atlantic; North Atlantic oscillation
• Online Access: http://hdl.handle.net/11104/0248914

We compare atmospheric circulation in six European regions from three long datasets: the reconstructed “EMULATE” (EMSLP) dataset spanning back to 1850, the NOAA “20th Century Reanalysis” (20CR) available since 1871, and the ECMWF ERA-20C Reanalysis since 1900. These long datasets are further compared with circulation from 6 reanalyses in the latter half of the 20th century. Circulation is described by indices of flow strength, flow direction, and vorticity, calculated using mean daily sea-level pressure. We used these indices to classify daily circulation into pre-defined circulation types. We studied seasonal changes in the frequency of circulation types, as well as the overall and within-type changes of circulation indices. Circulation types and indices from different databases correspond with each other very well over the British Isles and Baltic region, especially in winter. The least accord is generally in summer, namely in the Mediterranean. The most prominent trend since the mid-19th century is the one connected with a shift towards a positive phase of winter North Atlantic Oscillation (NAO) since the 1960s: increasing occurrence of the SW type over the British Isles and of the W type in Central Europe at the expense of S and cyclonic types. Increasing NAO further resulted in an increase of flow strength especially from the westerly sectors, and a shift towards more westerly flow in types classified as NW, SW, and S. Within-type trends of circulation indices also play a significant role in the overall picture of atmospheric circulation. The three long datasets of gridded sea-level pressure proved useful for representing atmospheric circulation over large parts of Europe. However, some long-term trends found in one database are not always present in the others.